Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. e5/3...c5/4. c3/4...Nc6/5. Nf3/5...Qb6/6. Bd3

=French Defence: Advance Variation=

White develops the light-squared bishop to d3. While he appears to have lost a pawn, 6... cxd4 7. cxd4 Nxd4? 8. Nxd4 Qxd4?? 9. Bb5+! will win Black's queen. Black usually plays 6...cxd4 7.cxd4 Bd7!, blocking the king from the Bb5+ and thus threatening to win the d4-pawn. White then usually plays a gambit. Note that 6...Bd7?! allows White the option of 7.dxc5! Bxc5 when Black does have to be careful - 8.O-O Ne7?? 9.b4!, trapping the bishop, shows that Black must be very careful. So 6...cxd4 is considered better, avoiding the tricks after 7.dxc5!

Theory table
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'''1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Nc6 5.Nf3 Qb6 6. Bd3'''